A known system for treating exhaust gas passing through an exhaust system of a diesel engine comprises a diesel oxidation catalyst (DOC) associated with a diesel particulate filter (DPF). The combination of these two exhaust gas treatment devices promotes chemical reactions in exhaust gas and traps diesel particulate matter (DPM) as exhaust flows through the exhaust system from the engine, thereby preventing significant amounts of pollutants such as hydrocarbons, carbon monoxide, soot, SOF, and ash, from entering the atmosphere.
A DPF requires regeneration from time to time in order to maintain engine performance. An engine control system typically estimates or infers particulate loading to determine if regeneration needs to be forced when the particulate loading reaches a level that is deemed excessive. However, regeneration can occur passively when conditions are favorable.
Regeneration is forced by creating conditions that will burn off trapped particulates. The creation of conditions for initiating and continuing regeneration typically involves elevating the temperature of exhaust gas entering the DPF to a suitably high temperature. Because a diesel engine typically runs relatively cool and lean, the post-injection of diesel fuel can be used as part of the strategy to elevate exhaust gas temperatures entering the DPF while still leaving excess oxygen for burning the trapped particulate matter.
Elevating exhaust temperature in that way for the purpose of regenerating a DPF decreases motor vehicle fuel efficiency. Furthermore, the manner in which a motor vehicle engine is being operated influences the regeneration process from the standpoints of both quality of regeneration and duration of regeneration. For example, a requested regeneration that seeks to reduce the amount of trapped matter to a target level may be terminated before the target is achieved (incomplete regeneration), or at an extreme the regeneration may fail entirely due to failure to achieve suitable exhaust conditions.
For evaluating a regeneration, a known strategy in effect calculates a rate at which trapped matter is being turned off by measuring, or estimating, the amount of matter burned off during a specified time interval. If the rate is sufficiently high, it is assumed that a satisfactory regeneration is occurring, and the regeneration is allowed to continue instead of being aborted. If the rate is not sufficiently high, it is assumed the regeneration should be aborted.
The inventors believe that a more robust strategy would be beneficial.